Conventionally, in an apparatus such as a copying machine, a scanner, a printer, and a multi-function device having a plurality of functions for serving as such apparatuses, there is known a configuration being provided with an ADF (Auto Document Feeder) that conveys a sheet (an original document) from a feed tray to a discharge tray along a sheet conveying path. Examples of such configuration are proposed in JP-A-2005-247575 (counterpart U.S. patent application is published as US 2005/0212195 A1) and JP-A-2005-253013 (counterpart U.S. patent application is published as US 2005/0194731 A1). The ADF disclosed in JP-A-2005-247575 and JP-A-2005-253013 is schematically shown as ADF 130 in FIG. 23. A simple overview of the mechanism and operation of the ADF 130 will be described below.
The conventional ADF 130 shown in FIG. 23 has a sheet feeding mechanism 131 that separates a plurality of sheets (hereinafter, referred to as a “stack of sheets”) placed on a feed tray 132 and sequentially feeds the stack of sheets to a sheet conveying path 138. The sheet feeding mechanism 131 is configured such that a feed chute portion 133 is formed monolithically from the feed tray 132, and a feed roller 134, a feed nip piece 135, a separation roller 136, and a separation nip piece 137 are arranged in the feed chute portion 133.
The feed roller 134 is rotatably arranged on a lower guide surface of the feed chute portion 133. The feed nip piece 135 is arranged on a portion of an upper guide surface of the feed chute portion 133 in a position facing the feed roller 134, such that the feed nip piece 135 is contactable with the teed roller 134. The feed nip piece 135 is urged toward the feed roller 134 to be in Contact with the feed roller 134 by an urging member that is not shown.
The stack of sheets placed on the feed tray 132 are urged toward the feed roller 134 by the feed nip piece 135 and a bottommost sheet of the stack of sheets that contacts the feed roller 134 is fed in a sheet feeding direction due to the rotation of the feed roller 134. In the configuration shown in FIG. 23, the sheets are placed on the feed tray 132 with its right face (face to be scanned) facing downward.
The separation roller 136 is rotatably arranged on the lower guide surface of the feed chute portion 133 to be spaced from the feed roller 134 in the sheet feeding direction. The separation nip piece 137 is arranged on the upper guide surface of the feed chute portion 133 that is a position facing the separation roller 136, such that the separation nip piece 137 contacts the separation roller 136. The separation nip piece 137 is urged toward the separation roller 136 to be in contact with the separation roller 136 by an urging member that is not shown. A sheet fed by the feed roller 134 is nipped between the separation roller 136 and the separation nip piece 137 and conveyed in the sheet feeding direction by the rotation of the separation roller 136.
The sheet conveying path 138 is configured to have a substantially U-lettered shape when viewed from a side of the ADF 130 and is provided at a position downstream with respect to the feed chute portion 133 in the sheet feeding direction. A conveying roller 139 is arranged on the sheet conveying path 138 and three pinch rollers 140 (140a, 140b, and 140c) are arranged on an outer circumference of the conveying roller 139. Each of the pinch rollers 140 are urged toward the conveying roller 139 by an urging member, which is not shown, to be in contact with the conveying roller 139.
A sheet fed to the sheet conveying path 138 by the sheet feeding mechanism 131 is conveyed along the sheet conveying path 138 while being nipped between the pinch roller 140a, which is disposed immediately upstream of a platen glass 142, and the conveying roller 139. The sheet is guided by a guide member 141 and conveyed onto the platen glass 142. At this time, an image formed on the sheet that is conveyed above the platen glass 142 is scanned by an image sensor 143 arranged below the platen glass 142.
The sheet having been scanned is conveyed upward while being nipped between the pinch roller 140b, which is disposed immediately downstream of the platen glass 142, and the conveying roller 139. At this time, the sheet is guided by a curved guide surface, which is not shown, and conveyed to perform a U-turn along an outer circumferential surface of the conveying roller 139.
The pinch roller 140c is arranged on the sheet conveying path 138 at a position most downstream. As shown in FIGS. 24A-24C, the pinch roller 140c is disposed vertically above the conveying roller 139 and supported by an outer guide 147 with the pinch roller 140c being urged toward the conveying roller 139 by a coil spring 146. A sheet is conveyed while being nipped between the pinch roller 140c and the conveying roller 139, to thereby be discharged to a discharge tray 144 from the sheet conveying path 138 through a discharge chute portion 145.
In the ADF 130 configured as described above, sheets are fed one by one from the stack of sheets placed faced down on the feed tray 132. The fed sheets are sequentially conveyed to the discharge tray 144 disposed above the feed tray 132. Accordingly, the sheets are stacked on the discharge tray 144 in an order (hereinafter, referred to as “reverse order”) reverse to an original order initially being stacked. In order to prevent the sheets from being thus discharged in reverse order, the conventional ADF disclosed in JP-A-2005-247575 and JP-A-2005-253013 is provided with, as shown in FIG. 24, a plate spring piece 148 that lifts up the discharged sheet from a nip position that is configured between the pinch roller 140c and the conveying roller 139.
According to this configuration, the sheet S2 (hereinafter, referred to as a “subsequent sheet”) that is discharged by the pinch roller 140c and the conveying roller 139 subsequent to the discharged sheet is guided such that a leading edge of the subsequent sheet S2 is placed, by the plate spring piece 148, beneath a trailing edge of the preceding discharged sheet S1 (hereinafter, referred to as a “preceding sheet”) . Then, the subsequent sheet S2 is further conveyed, to thereby be discharged to slide beneath the preceding sheet S1. Accordingly, the sheets discharged onto the discharge tray 144 will be stacked in the original order.
According to the ADF 130 having the plate spring piece 148, the order of the discharged sheets is not reversed as described above. However, in the conventional ADF 130, concerns arise about the possible occurrence of an event that due to an amount of the preceding sheets stacked on the discharge tray 144, or an aged deterioration of the roller surface of the pinch roller 140c, the subsequent sheet may not be placed beneath the preceding sheets stacked on the discharge tray 144 and may be discharged between the stacked sheets or on the top of the stacked sheets.
For example, when the amount of sheets discharged on the discharge tray 144 increases, as shown in FIG. 25, a subsequent sheet S3 is prevented from advancing by the preceding sheets S1 and S2 that are already being discharged, and thus, the subsequent sheet S3 is immediately stopped after a conveying force applied by the nip roller 140c and the conveying roller 139 is lost. At this time, a trailing edge of the sheet S3 remains near the nip position. The trailing edge remaining near the nip position may be scraped upward by the pinch roller 140c, however, when the roller surface of the pinch roller 140c is in a slippery condition due to an aged deterioration, the trailing edge of the sheet S3 may not be scraped upward. When another subsequent sheet S4 is discharged with the trailing edge of the sheet S3 remaining near the nip position, the subsequent sheet S4 is discharged at a higher position than the preceding sheet S3, causing a problem that the order of the discharged sheets may not be the original order. In addition, the subsequent sheet S4 may collide with the trailing edge of the preceding sheets, thereby causing a jam of the sheets (paper jam).